Variable air induction apparatuses are conventionally used to improve a torque of an internal combustion engine by varying a length of an air intake passage in accordance with a number of revolutions of the internal combustion engine. In these variable air induction apparatus, the length of the air intake passage is increased when the number of revolutions of the internal combustion engine is relatively small, and the length of the air intake passage is decreased when the number of revolutions of the internal combustion engine is relatively large, to improve the torque of the internal combustion engine.
In a variable air induction apparatus disclosed in JP-2002-147299-A, for example, a valve element is installed in a short air intake passage to open and close the short air intake passage. When a long air intake passage is used, the valve element closes the short air intake passage. When the short air intake passage is used, the valve element opens the short the air intake passage.
In another variable air induction apparatus disclosed in JP-2002-256874-A, a valve element is located at a connection portion of a short air intake passage and a long air intake passage. When the long air intake passage is used, the valve element opens the long air intake passage and closes an end portion of the short air intake passage. When the short air intake passage is used, the valve element closes an end portion of the long air intake passage and opens the short air intake passage.
However, in the variable air induction apparatus disclosed in JP-2002-147299-A, the valve element closes only the short air intake passage, so that the long air intake passage is opened at all times, regardless of the number of revolutions of the internal combustion engine. Thus, while the valve element is opening the short air intake passage for using the short air intake passage, the intake air flows not only in the short air intake passage but also in the long air intake passage. As a result, undesirable intake air pulsation occurs not only in the short air intake passage but also in the long air intake passage, to decrease an air intake efficiency.
In the variable air induction apparatus disclosed in JP-2002-256874-A, while one of the short air intake passage and the long air intake passage is opened, the other of them is closed, so that undesirable intake air pulsation does not occur, not to decrease the air intake efficiency. However, in the variable air induction apparatuses with a construction to open the one of the short and long air intake passages and to close the other of them as disclosed in JP-2002-256874-A, the valve element has a cantilever construction that rotates around a supporting point at one end side thereof. The valve element with the cantilever construction is much affected by the pulsation of the intake air flowing in the air intake passages. Thus, it is necessary to apply a relatively large force from a driving device to the valve element to keep the valve element at a specific position. This increases a size of the driving device and a size of the variable air induction apparatus.